Novel PWM inverter output active filter for common-mode voltage cancellation

MA Hong-fei Pulse width modulated (PWM) inverter can generate common-mode voltage, which can produce charge-discharge current at the distant of every insulated gate bipolar transistor (IGBT) high-speed switching. This current creates ground current escaping to earth through stray capacitors inside motors. The large ground current can create electromagnetic interference, shorten the life of motor bearings and effect reliability of the whole system. This paper proposes a novel PWM inverter output active filter for common-mode voltage reduction. This active filter which consists of a single-phase inverter and a five windings common mode transformer can produce the same amplitude as, but opposite polarity to the common mode voltage generated by the PWM inverter, and superimpose this voltage to the output of the PWM inverter by the five windings common mode transformer, then common mode voltage applied to the load can be canceled effectively. This filter has a simple configuration, and is easy to be controlled. Theoretical analysis, simulation and experiment results are presented to verify the effectiveness of the proposed method.